The present invention relates to wireless communication devices such as mobile phones. The first Global System for Mobile (GSM) communication networks were designed for voice services rather than for data services. When the use of GSM data services started, it soon became evident that the Circuit Switched (CS) bearer services were not well-suited for certain types of applications with a bursty nature. Therefore the new Packet Switched (PS) data transmission service GPRS (General Packet Radio Service) was developed for packet services. GPRS is a packet radio network utilizing the GSM network, and GPRS endeavours to optimize data packet transmission by means of GPRS protocol layers on the air interface between a mobile station (hereinafter also called a mobile terminal) and a GPRS network.
A GPRS mobile station (MS), also called a mobile terminal, can operate in one of three modes of operation, as described in 3GPP TS 23.060, “Service description; Stage 2,” Section 5.4.5. This document 3GPP TS 23.060, v 5.6.0, General Packet Radio Service (GPRS), Service Description is useful for understanding the context of the present invention, in addition to 3GPP TS 43.055, v 5.2.0, Radio Access Network, Dual Transfer Mode.
The three modes are Class-A Mode, Class-B Mode, and Class-C Mode. According to the Class-A mode of operation, the MS is attached to both GPRS as well as other GSM services, and therefore Class-A Mode corresponds to Dual Transfer Mode (DTM) (hereinafter also called dual mode). The mobile user in Class-A Mode can make and/or receive calls on the two services simultaneously, for example having a normal GSM voice call and receiving GPRS data packets at the same time. According to the Class B mode of operation, the MS is attached to both GPRS and other GSM services, but the MS can only operate one set of services at a time. According to the Class C mode of operation, the MS can only be attached either to the GSM network or the GPRS network; the selection is done manually and there are no simultaneous operations.
Based on the current standard (3GPP TS 44.018, “Radio Resource Control Protocol”), when the MS releases a CS connection (also referred to as a radio resource or RR connection) while in the Dual Transfer Mode (DTM), all packet resources are aborted. This is illustrated in FIG. 1 (also see 3GPP TS 43.064, “Overall description of the GPRS radio interface; Stage 2”), which shows RR operating modes and transitions between Class-A (DTM supported) and Class-B. An RR Release moves the MS from the Dual Transfer Mode 102 into an Idle/Packet Idle state 104, after which the MS must then obtain packet access in order to perform packet transfer. In other words, after the release of the CS connection, the MS is in the packet idle mode and must perform a complete acquisition of system information and ask for PS resources again, in order to get into the Packet Transfer Mode 106.
In any GSM network, there will be several BSCs (Base Station Controllers). When implementing GPRS, a software and hardware upgrade of this unit is required. The hardware upgrade consists of adding a Packet Control Unit (PCU). This extra piece of hardware differentiates data destined for the standard GSM network or Circuit Switched Data and data destined for the GPRS network or Packet Switched Data. In some cases a PCU can be a separate entity.
According to the current GSM/GPRS standardization, a mobile station (MS) can have a GSM circuit switched (CS) speech connection and a GPRS/EGPRS packet switched (PS) data connection simultaneously in active use only if one of the following is true: the MS represents a “class A” GPRS mobile that can handle both CS and PS connections simultaneously without radio resource coordination between the CS and PS domains; or the MS and the network support the Dual Transfer Mode (DTM) feature that provides radio resource coordination between the CS and PS domains.
The implementation of a “Class A” mobile station would basically require a mobile terminal with two radio parts, resulting in a high development cost, which mobile manufacturers would like to avoid. Nevertheless, there is a clear need for this type of mobile device that can have a GSM circuit switched (CS) speech connection and a GPRS/EGPRS packet switched (PS) data connection simultaneously in active use, because some services demand the simultaneous existence of a CS connection and a PS data transfer. This fact has given a strong impetus for the “class B” DTM feature implementation.
DTM is a standardized feature that provides simultaneous GSM/GPRS service for GPRS/EGPRS mobile stations in a coordinated manner. In other words, a DTM-capable MS can have a CS speech connection as well as a PS data transfer ongoing at the same time if the radio timeslots allocated in each direction are contiguous and within the same frequency. This kind of radio resource coordination between the CS and PS resource allocations should be provided by the network that supports the DTM functionality.
Current DTM-specifications state that the dual transfer mode (i.e. the DTM mode where the MS is having a CS and a PS radio resource at the same time) can be entered only from dedicated mode, which is the mode where the MS is having a CS connection. This means that the DTM resource coordination is especially needed in a situation where a PS data connection needs to be established for a DTM-capable MS that happens to be in dedicated mode.
In the GSM/GPRS networks it is the Base Station Subsystem (BSS) that takes care of radio resource management functions. However, the CS and PS radio resources are managed by different network entities: the directory exchange (DX) takes care of CS radio resources and the Packet Control Unit (PCU) takes care of PS radio resources.
From the BSS perspective, the PCU has to know whether the MS happens to have a CS connection ongoing or not when there is a need for a PS data transfer. If the MS is not having a CS connection, then normal PS data transfer procedures can be applied. However, if the MS has an ongoing CS connection, then DTM-specific data transfer procedures are needed.
This means that the DX and the PCU need to communicate with each other so that information about the DTM mobiles' resource allocations can be shared between the PS and CS domains. This requires internal signaling at the BSS. The main problem with this existing technology is that the PCU has to know whether a DTM-capable MS happens to have a CS connection ongoing or not, when there is a need for a PS data transfer. When a PS data transfer is established in the uplink (UL) direction, then there is no problem. If the MS has a CS connection ongoing, then it uses a DTM-specific channel request message when it requests a PS radio resource. Based on this message the network knows that DTM resource coordination is needed.
In the downlink (DL) direction, however, the PCU may receive data packets addressed to a DTM-capable MS whose current mode (dedicated mode or idle mode) is not known. There are two straightforward prior art means to find out the mode of the MS: (I) the PCU asks the DX, when needed, whether the MS is in dedicated mode; or (II) the DX informs the PCU whenever a DTM-capable MS enters or leaves dedicated mode so that the PCU can keep a record about all DTM mobiles that are having a CS connection within a given network area.
The problem with the first method (I) is that the PCU has to make such queries very often, because a PS data transfer establishment is a very frequent procedure and also because the PCU cannot really know whether the MS is in dedicated mode or in idle mode. On the other hand, it is rather improbable that a MS will happen to have a CS connection ongoing when a data packet arrives at the PCU (a typical traffic load generated by a GSM subscriber is 25 mErl, meaning that the subscriber is having a speech connection active only 2.5% of the time).
The problem with the second method (II) is that the DX does not know whether the MS is even attached to the GPRS network. Therefore, the DX has to inform the PCU about all DTM-capable mobiles. As a result, the DX has to send a large amount of information messages to the PCU, because the CS connection establishment and release procedures are very common procedures at the BSS. On the other hand, it is rather improbable that a MS will receive any data packets during the CS connection; most of the mobiles are not even attached to the GPRS network when they are using the CS speech service.
In other words, the BSS has to perform DTM coordination for all DTM-capable mobile stations even if only a small minority of the DTM mobiles are really applying the DTM functionality (that is, having a CS and a PS connection in active use at the same time). This type of DTM coordination will generate a considerable signaling load within the BSS when the penetration of DTM-capable mobiles increases in the GSM networks.
If we assume that the mean GSM call holding time is 120 seconds, then we may estimate that a BSS with a CS traffic handling capacity of 4000 Erl generates about 2*4000/120 s≈70 CS call establishment and release procedures per second. If the DTM penetration is 80%, then in the second solution (II) the DX has to send about 50 DTM coordination messages per second to the PCU—and most of the messages are sent in vain.
It is well known for wireless networks to use mobility management (MM) in order to keep track of the position of a mobile station (MS). MM employs a combination of wireless hardware and associated subscriber information. Because a mobile station is often moving from one place to another, the network must be aware of the MS's position in order to maintain connectivity. Mobility management refers to the range of procedures that make this possible. These include identification and authentication of the mobile subscriber, security, access to wireless services, transfer of subscriber data among network nodes, location updating, and registration. Unfortunately, MM procedures have not been employed with respect to communications between a DX and PCU, or with respect to an MS's movement in and out of a DTM dedicated mode, which of course can occur even when an MS is perfectly still (i.e. not changing position).
Another problem with the DTM functionality is that when the MS needs to establish a CS connection (e.g. a speech call) when it has active packet data transfer ongoing, the MS releases the packet connection without any signaling to the network, and establishes the CS connection in the random access control channel (RACH). At this stage, the point of view of the PCU is that the MS has disappeared from the allocated packet resources, and the PCU issues a RADIO STATUS message towards the serving GPRS support node (SGSN). In case the MS has no uplink GPRS data to transmit to the network, the data flow in the downlink direction will be halted even though the MS and the network are DTM-capable. These and other problems of the existing art can be solved by the present invention.